docs: def get_lower_triangle_correlation_matrix(self, sites, imt):
          """
          Get lower-triangle matrix as a result of Cholesky-decomposition
          of correlation matrix.
  
          The resulting matrix should have zeros on values above
          the main diagonal.
  
          The actual implementations of :class:`BaseCorrelationModel` interface
          might calculate the matrix considering site collection and IMT (like
          :class:`JB2009CorrelationModel` does) or might have it pre-constructed
          for a specific site collection and IMT, in which case they will need
          to make sure that parameters to this function match parameters that
          were used to pre-calculate decomposed correlation matrix.
  
          :param sites:
              :class:`~openquake.hazardlib.site.SiteCollection` to create
              correlation matrix for.
          :param imt:
              Intensity measure type object, see :mod:`openquake.hazardlib.imt`.
          """
          return numpy.linalg.cholesky(self._get_correlation_matrix(sites, imt))